Lecture 2 3 Compression, Condition Assess

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  • Lecture 2 3 Compression, Condition Assess

    1. 1. Classnotes for ROSE School Course in: Masonry Structures Notes Prepared by: Daniel P. Abrams Willett Professor of Civil Engineering University of Illinois at Urbana-Champaign October 7, 2004 Lesson 2 and 3: Properties of Masonry Materials Introduction, compressive strength, modulus of elasticity condition assessment, movements
    2. 2. Historical Use of Masonry as a Structural Material
    3. 3. The First Building Material <ul><li>The first masonry structures were constructed of mud, sun-dried brick. </li></ul><ul><li>The people of Jericho were building with brick more than 9000 years ago. </li></ul><ul><li>Sumerian and Babylonian builders covered brick walls with kiln-baked glazed brick. </li></ul><ul><li>Mesopotamian builders constructed temple towers from 4000 BC to 600 BC. </li></ul>Etemenanki Ziggurat height 91 meters
    4. 4. The First Building Material <ul><li>Stone masonry was used for Egyptian pyramids c. 2500 BC. </li></ul><ul><li>Pyramid of Khufu at Giza measured 147 m. high and 230 m. square. </li></ul><ul><li>Pyramid of Khafre at Giza was constructed without cranes, pulleys or lifting tackle. No mortar or adhesive was used. </li></ul><ul><li>Ancient examples of Cyclopean masonry found throughout Europe, China and Peru. </li></ul><ul><li>Egyptian houses made of mud- brick walls. </li></ul>Pyramid of Khafre at Giza
    5. 5. Greek and Roman Architecture <ul><li>Early Greek architecture (3000 to 700 BC) used massive stone blocks for walls, and early vaults and domes. </li></ul><ul><li>Greeks constructed with limestone and marble. </li></ul><ul><li>Romans constructed with concrete, terra cotta and fired clay bricks. </li></ul><ul><li>Romans refined arch, vault and dome construction to construct great aqueducts, coliseums and palaces were built with clay brick. </li></ul>El Puente Aqueduct near Segovia Spain 1st Century AD two tiers of arches 28. 5m tall
    6. 6. Applications in China Great Wall of China 6 to 15m. tall 4.6 to 9.1m wide at base ave. 3.7 m wide at top <ul><li>The Great Wall of China was constructed from 221 to 204 BC. </li></ul><ul><li>The wall winds 2400 km from Gansu to the Yellow Sea, and is the longest human-made structure in the world. </li></ul><ul><li>The wall is constructed of earth and stone with a brick facing in the eastern part. </li></ul>
    7. 7. Byzantine Architecture <ul><li>Huge domed churches were built on a scale far larger than achieved with the Romans. </li></ul><ul><li>Innovative Byzantine technology allowed architects to design a basilica with an immense dome over an open, square space. </li></ul><ul><li>Isalmic architects developed a rich variety of pointed, scalloped, horseshoe and S-curved arches for mosques and palaces. </li></ul>Hagia Sophia, Istanbul constructed 532-537 AD dome fell after earthquake in 563
    8. 8. Masonry in the Americas Pyramid of the Sun Teotihuacan Mexico 66-m. high 2nd century AD <ul><li>Early pyramids built c. 1200 BC at the Olmec site of LaVenta in Tabasco Mexico. </li></ul><ul><li>Later monuments constructed by the Maya, Toltecs and Aztecs in central Mexico, the Yucatan, Guatemala, Honduras, El Salvador and Peru were based on the Olmec plan. </li></ul><ul><li>Four-sided, flat-topped polyhedrons with stepped sides. </li></ul>
    9. 9. Masonry in the Americas Pueblo Bonito Chaco Canyon , NM 10th Century AD covers more than 3 acres <ul><li>Aztec, Mayan and other Indian cultures relied on masonry for housing and monuments. </li></ul><ul><li>Stone veneers used by Mayans at Uxmal in 9th century. Slight outward lean of these buildings made them appear light and elegant. </li></ul><ul><li>Pueblo Bonito housed up to 1000 residents. </li></ul><ul><li>Anasazi constructed multistory pueblos from stone, mud and beams during period of 1100-1300 AD. </li></ul>
    10. 10. Romanesque, Gothic and Renaissance Santa Maria degli Angeli Firenza, Italy constructed 1420-61 AD 39 m. in diameter, 91 m. high Filippo Brunelleschi <ul><li>With Romanesque architecture (10th to 12th century), large internal spaces were spanned with barrel vaults supported on thick, squat columns and piers. </li></ul><ul><li>Gothic architecture (12th to 16th century) used a pointed arch which minimized outward thrust and resulted in lighter and thinner walls. </li></ul><ul><li>Renaissance architecture was influenced by the round arch, the barrel vault, and the dome. </li></ul>
    11. 11. Masonry at the Turn of the Century <ul><li>URM brick bearing-wall construction used for multistory buildings. Design based on empirical rules. </li></ul><ul><li>URM construction popular for low-rise buildings in inner core of cities, many of which are still standing today. </li></ul><ul><li>In 1908, the Nat. Assoc. of Cement Users developed the first specification for concrete block. Fifty million cmu’s produced in 1919 which grew to 467 million in 1941. </li></ul>Monadnock Building Chicago, 1891 D. Burnham and J. Root
    12. 12. Rational Structural Design <ul><li>Masonry compressive strength standardized by 1910. </li></ul><ul><li>Empirical design still prominent through first half of twentieth century. </li></ul><ul><li>Research on structural masonry done at the Structural Clay Products Association and Portland Cement Association. </li></ul><ul><li>BIA in the 1966 and NCMA in 1970 developed standards for structural design of brick and block. </li></ul>code of Hammurabi Babylon, 1780 BC
    13. 13. Recent Code Developments <ul><li>TMS developed first standard for brick/block masonry, and became Chapter 24 of 1985 UBC. Further revised in 1988, 1991 and 1994 (as Chapter 21). </li></ul><ul><li>ACI-ASCE 530 code published in 1988. Further revised in 1992 and 1995 as MSJC code. </li></ul><ul><li>Strength design introduced into 1985 UBC. </li></ul><ul><li>New chapter on strength design in 2002 MSJC. </li></ul>MSJC Building Code Requirements for Masonry
    14. 14. Masonry Seismic Provisions <ul><li>Chapters 8 and 8A of NEHRP Recommended Seismic Provisions for New Buildings (FEMA 222A, 1994) </li></ul><ul><li>Appendix C of NEHRP Handbook for Seismic Evaluation of Existing Buildings (FEMA 178, 1992) </li></ul><ul><li>FEMA 273/356 Guidelines for Seismic Rehabilitation of Buildings </li></ul>NEHRP Provisions for New Buildings
    15. 15. Present Applications <ul><li>The use of masonry as a structural material has been developing rapidly in the western US over the last two decades. </li></ul><ul><li>Tall buildings of structural masonry are now being constructed. </li></ul><ul><li>A slow revolution in the east. </li></ul><ul><li>URM still used for new construction. </li></ul><ul><li>Tall, slender walls compete with tilt-up construction. </li></ul>Excaliber Hotel, Las Vegas tallest building of structural masonry
    16. 16. Masonry Compressive Strength
    17. 17. Mechanics of Masonry in Compression t j t b P P masonry unit l stresses shown for  mortar >  unit mortar
    18. 18. Biaxial Strength of Masonry Units direct tensile strength of unit from test f’ udt f’ udt f’ udt f’ ut flat-wise compressive strength of unit from test f’ ut f’ ut brick splits when: compression tension
    19. 19. Biaxial Strength of Mortar multiaxial compressive strength mortar crushes when: 4.1 1.0 compression compression uniaxial compressive strength from test f’ jt f’ jt
    20. 20. Masonry Compressive Strength equilibrium relation: t j t b P P if mortar crushes: if brick splits:
    21. 21. Masonry Compressive Strength if mortar crushes and brick splits simultaneously: where U u = coefficient of non-uniformity (range 1.1 to 2.5) Hilsdorf equation
    22. 22. Nonlinear Mortar Behavior triaxial test 1000 psi v l 1000 psi 30 psi
    23. 23. Unit Splitting vs. Mortar Crushing Linear Mortar f’ udt unit failure envelope mortar failure envelope tension compression unit stress path mortar stress path mortar crushes failure f’ jt f’ ut
    24. 24. Unit Splitting vs. Mortar Crushing Nonlinear Mortar tension compression f’ udt mortar failure envelope unit failure envelope failure unit stress path mortar stress path unit splits f’ ut f’ jt
    25. 25. Incremental Lateral Tensile Stress on Masonry Unit From Atkinson and Noland “A Proposed Failure Theory for Brick Masonry in Compression ,” Proceedings, Third Canadian Masonry Symposium, Edmonton, 1983, pp. 5-1 to 5-17. Assuming linear behavior for masonry unit, and nonlinear mortar behavior:
    26. 26. Effect of Mortar on Compression <ul><li>weaker mortars result in weaker prism strength because ratio of v mortar /v unit is larger </li></ul><ul><li>weaker mortars result in greater extents of nonlinear prism behavior </li></ul>M S N O Weaker Mortars
    27. 27. <ul><li>may not adhere to units as well. </li></ul><ul><li>a larger scatter of experimental data with the stronger mortars. </li></ul><ul><li>create a stiffer prism which is more sensitive to alignment problems during testing and more brittle. </li></ul><ul><li>more variable masonry compressive strength. </li></ul>Effect of Mortar on Compression M S N O Stronger Mortars
    28. 28. Guidelines for Prism Testing <ul><li>A set of five prisms shall be built and tested prior to construction in accordance with UBC Std. 21-17. </li></ul><ul><li>At least three prisms per 5,000 sq. feet of wall area shall be built and tested during construction. </li></ul><ul><li>Test values for prism strength shall exceed design values. </li></ul>UBC Sec. 2105.3.2: Masonry Prism Testing Note that testing is not required if half of allowable stresses are used for design. NCMA TEK 18-1 Concrete Masonry Prism Testing
    29. 29. <ul><li>Methods for prism construction, transportation and curing. </li></ul><ul><li>Preparation for testing, test procedures, etc. </li></ul><ul><li>Calculation for compressive stress. Net area, correction factors. </li></ul>Guidelines for Prism Testing UBC Standard 21-17: Test Method for Compressive Strength of Masonry Prisms prism h/t p correction factor Table 21-17A 1.3 1.5 2.0 2.5 3.0 4.0 5.0 0.75 0.86 1.00 1.04 1.07 1.15 1.22 Use lesser of average strength or 1.25 times least strength. h t p
    30. 30. Code Values for Prism Strength <ul><li>Use test values per UBC 21-17. </li></ul><ul><li>Take f’ m equal to 75% of average prism record value. (2105.3.3) </li></ul><ul><li>Take f’ m from Table 21-D if no prisms are tested. </li></ul>UBC Sec. 2105.3.4: Unit Strength Method Associated BIA Technical Note: 35 Early Strength of Brick Masonry
    31. 31. Compressive Strength of Masonry per UBC UBC Table 21-D Type M/S mortar Type N mortar 14,000 or more 12,000 10,000 8,000 6,000 4,000 5,300 4,700 4,000 3,350 2,700 2,000 4,400 3,800 3,300 2,750 2,200 1,600 Specified compressive strength of clay masonry, f’ m Specified Compressive Strength of Masonry, f’ m , (psi) Compressive Strength of Clay Masonry Units (psi)
    32. 32. Compressive Strength of Masonry per UBC UBC Table 21-D Type N mortar 3,000 2,500 2,000 1,500 1,000 2,800 2,350 1,850 1,350 950 Specified compressive strength of concrete masonry, f’ m Type M/S mortar 4,800 or more 3,750 2,800 1,900 1,250 Specified Compressive Strength of Masonry, f’ m , (psi) Compressive Strength of Concrete Masonry Units (psi)
    33. 33. MSJC Specifications for Prism Strength <ul><li>Sec. 1.4.B Compressive Strength Determination </li></ul><ul><li>Sec. 1.4B.2 Unit Strength method </li></ul><ul><ul><li>Table 1 Compressive Strength for Clay Masonry </li></ul></ul><ul><ul><li>Table 2 Compressive Strength for Concrete Masonry </li></ul></ul><ul><li>Sec. 1.4B.3 Prism Test Method </li></ul><ul><ul><li>ASTM C 1314 </li></ul></ul>
    34. 34. Compressive Strength of Masonry per MSJC MSJC Specification Table 1 Net Area Compressive Strength of Clay Masonry Units (psi) Type M/S Mortar Type N Mortar Net Area Compressive Strength of Masonry ( psi) 1,700 3,350 4,950 6,600 8,250 9,900 13,200 2,100 4,150 6,200 8,250 10,300 - - 1,000 1,500 2,000 2,500 3,000 3,500 4,000 Compressive strength of clay masonry by unit strength method
    35. 35. Compressive Strength of Masonry per MSJC MSJC Specification Table 2 Compressive Strength of Concrete Masonry Units (psi) Type M/S Mortar Type N Mortar Net Area Compressive Strength of Masonry (psi) 1,250 1,900 2,800 3,750 4,800 1,300 2,150 3,050 4,050 5,250 1,000 1,500 2,000 2,500 3,000 Compressive strength of concrete masonry by unit strength method MSJC values of compressive strength from Table 1 and Table 2 are intended to be used in lieu of prism tests to estimate needed mortar types and unit strengths for a required compressive strength.
    36. 36. Comparison of Default Prism Strengths UBC Table 21-D vs. MSJC Specifications Table 1 Default prism strengths are lower bounds to expected values.
    37. 37. Comparison of Default Prism Strengths UBC Table 21-D vs. Table 2 MSJC-Spec. Note: MSJC and UBC values are almost identical for concrete masonry. Default prism strengths are lower bounds to expected values.
    38. 38. Masonry Elastic Modulus
    39. 39. Elastic Modulus of Masonry in Compression Basic Mechanics  t j t b P =  y A net [1] [2] [3] [4] [5] [6] [7]
    40. 40. Elastic Modulus of Masonry in Compression Basic Mechanics Reference: Structural Masonry by S. Sahlin, Section D.2 [8]  t j t b P =  y A net [12] [9] [10] [11]
    41. 41. Elastic Modulus of Masonry in Compression 1.2 concrete block masonry clay-unit masonry 0.76 0.0 0.2 0.4 0.6 0.8 1.0 0 0.5 1 1.5 2  t = 0.0498 (typical for concrete block masonry)  t = 0.152 (typical for brick masonry)
    42. 42. Code Assumptions for Elastic Modulus UBC Sec. 2106.2.12 and 2106.2.13 & MSJC Sec. 1.8.2.2.1 and 1.8.2.2.2 secant method f m  m MSJC Sec. 1.8.2.1.1 for clay-unit masonry E m = 700 f’ m for concrete-unit masonry E m = 900 f’ m UBC 2106.2.13 MSJC Sec. 1.8.2.2.2 G = 0.4 E m estimate without prism test data UBC Sec. 2106.2.12.1 for clay-unit or concrete masonry E m = 750 f’ m < 3000 ksi f’ mt E m 0.33 f’ mt 0.05 f’ mt
    43. 43. Strength of URM Bearing Walls
    44. 44. Unreinforced Bearing and Shear Walls <ul><li>resist vertical compression </li></ul>Structural Walls have 3 functions: Ref: BIA Tech. Note 24 The Contemporary Bearing Wall <ul><li>resist bending from eccentric vertical loads and/or transverse wind, earthquake, or blast loads </li></ul><ul><li>resist in-plane shear and bending from lateral loads applied to building system in direction parallel with plane of wall </li></ul>in-plane shear and moment (shear wall) transverse loads (out-of-plane wall) floor or roof loads (bearing wall)
    45. 45. Unreinforced Bearing and Shear Walls Historically walls were sized in terms of h/t ratio which was limited to 25. Empirical design of masonry UBC 2105.2 h < 35 ’ Associated BIA Technical Note: 24 series The Contemporary Bearing Wall Building wind = 15 psf h
    46. 46. Concentric Axial Compression Buckling Load Euler buckling load: P =  y A net t h’ = kl for rectangular section:
    47. 47. Concentric Axial Compression Note: for MSJC and UBC plot, r=0.289t is assumed h’/t 25 50 75 100  y 0.25 f’ m MSJC/UBC f’ m 24.8 Euler curve
    48. 48. Code Allowable Compressive Stress 0 0.1 0.2 0.3 0 50 100 150 200 for h’/r > 99 : F a = 0.25 f’ m [(70r/h’) 2 ] MSJC Eq. 2-13 and UBC Eq. 7-40 MSJC Section 2.2.3 and UBC Section 2107.3.2: for h’/r < = 99: F a = 0.25 f’ m [1 - (h’/140r) 2 ] MSJC Eq. 2-12 and UBC Eq. 7-39
    49. 49. Concentric Axial Compression UBC 2106.2.4: Effective Wall Height translation restrained no sidesway restraint MSJC 2.2.3: Buckling Loads e = eccentricity of axial load rotation restrained 2.0 rotation unrestrained 2.0 h’=kh rotation restrained 0.70 h rotation unrestrained 1.0 k = h’/h
    50. 50. Concentric Axial Compression UBC 2106.2.3: Effective Wall Thickness A. Single Wythe t = specified thickness t mortar or grout filled collar joint B. Multiwythe C. Cavity Walls each wythe considered separate both wythes loaded P 1 P 2 t 1 t 2 air space wire joint reinforcement P t 1 t 2 one wythe loaded
    51. 51. Concentric Axial Compression Neglect web area if face-shell bedding is used. UBC 2106.2.5: Effective Wall Area Effective area is minimum area of mortar bed joints plus any grouted area. face shell effective thickness raked joint effective thickness
    52. 52. Example: Concentric Axial Compression Determine the allowable vertical load capacity of the unreinforced cavity wall shown below per both the UBC and the MSJC requirements. Per NCMA TEK 14-1A for face shell bedding: A net = 30.0 in 2 I net = 308.7 in 4 r = 2.84 in. (r based only on loaded wythe) P a concrete footing 20’-0” Case “A”: Prisms have been tested. f’ m = 2500 psi for block wall f’ m = 5000 psi for brick wall Case “B”: No prisms have been tested. (Type I CMU’s and Type S mortar will be specified.) f’ m = 1500 psi for block wall metal ties face-shell bedding 7.63” 8”CMU 3.63” 4” brick
    53. 53. Example: Case “A” MSJC Section 2.2.3 & UBC 2107.3.2 * no buckling check per UBC. P a = 11.9 kip / ft for both codes MSJC Section 2.2.3: check buckling *
    54. 54. Example: Case “B” MSJC Section 2.2.3 & UBC 2107.3.2 MSJC Section 2.2.3: check buckling Governs for MSJC, take 1/2 for UBC since no special inspection is provided.
    55. 55. Eccentric Axial Compression Ref: NCMA TEK 14-4 Eccentric Loading of Nonreinforced Concrete Masonry h P e Pe t combined axial stress plus bending f a + f b -f a + f b axial stress P bending stress M = Pe
    56. 56. Eccentric Axial Compression References Associated NCMA TEK Note 31 Eccentric Loading of Nonreinforced Concrete Masonry (1971) Associated BIA Technical Note 24B Design Examples of Contemporary Bearing Walls 24E Design Tables for Columns and Walls where F a = allowable axial compressive stress (UBC 2107.3.2 or MSJC Sec. 2.2.3) F b = allowable flexural compressive stress = 0.33 f´ m (UBC 2107.3.3 or MSJC Sec 2.2.3) limiting compressive stress (controls for small e’s) UBC Section 2107.2.7 and MSJC 2.2.3: Unity Formula limiting tensile stress -f a + f b < F t where F t = allowable tensile stress (controls for large e’s) UBC 2107.3.5 or MSJC 2.2.3: Allowable Tensile Stress
    57. 57. Allowable Tensile Stresses, F t MSJC Table 2.2.3.2 and UBC Table 21-I 40 25 68* 80 50 80* 30 19 58* 60 38 60* 24 15 41* 48 30 48* 15 9 26* 30 19 29* * grouted masonry is addressed only by MSJC all units are (psi) Direction of Tension and Type of Masonry Mortar Type Portland Cement/Lime or Mortar Cement Masonry Cement/Lime M or S M or S N N tension normal to bed joints solid units hollow units fully grouted units tension parallel to bed joints solid units hollow units fully grouted units
    58. 58. Allowable Flexural Tensile Stresses, F t weak units flexural tension parallel to bed joints strong units No direct tensile strength assumed normal to head joints, just shear strength along bed joint. flexural tension normal to bed joints Note: direct tensile stresses across wall thickness is not allowed per UBC or MSJC.
    59. 59. Example: Eccentric Axial Compression f’ m = 2000 psi (from tests) Type S mortar Determine the allowable vertical load capacity per UBC and MSJC. Per NCMA Tek 141A: (per running foot) A net = 30.0 in 2 I x = 309 in 4 S x = 81.0 in 3 r= 2.84” F t = 25 psi per UBC 2107.3.5 and MSJC Table 2.2.3.2 e = 3.0” concrete footing 20’-0” P a 7.63” 8”CMU ungrouted face-shell bedding 1.25”
    60. 60. Example Tension controlling:
    61. 61. Example Compression controlling: UBC 2107.3.4 and MSJC 2.2.3
    62. 62. Example MSJC Section 2.2.3: Check Buckling (no buckling check per UBC) Code UBC MSJC P a (lbs) Tension Compression Buckling 6750 6233 6750 6233 ----- 1417
    63. 63. Kern Distance for URM Wall e = t/6 f a + f b e Assuming F t = 0 for solid section. -f a + f b = 0 t P = + f a f b b t/3 t b/3 kern If load is within kern, then no net tensile stress.
    64. 64. Kern Distance for URM Wall Specific Tensile Strength, F t , for solid section. f a + f b e -f a + f b = F t t P = + f a f b b t kern If load is within kern, then tensile stress < F t .
    65. 65. Strength of Walls with no Tensile Strength Resultant load inside of kern. f m P e P t
    66. 66. Strength of Walls with no Tensile Strength Neglect all masonry in tension. Note: This approach is outside of UBC and MSJC since F t may be exceeded. Partially cracked wall is not prismatic along its height. Stability of the wall must be checked based on Euler criteria modified to account for zones of cracked masonry. Analytical derivation for this case is provided in Chapter E of Structural Masonry by S. Sahlin. Resultant load outside of kern. P e t t/2 f m P [1] [2] [3] [4]
    67. 67. Example Part (a) e = 1.0 in. < t/6 = 1.27 in. within kern! Part (b) e = 2.5 in. > t/6 = 1.27 in. outside of kern! Determine the maximum compressive edge stress. e two-wythe brick wall P = 10 kip/ft. t = 7.63”
    68. 68. Condition Assessment
    69. 69. Insitu Material Properties <ul><li>Compressive strength </li></ul><ul><li>Elastic modulus </li></ul><ul><li>Flexural tensile strength </li></ul>
    70. 70. Insitu Material Properties <ul><li>Shear strength </li></ul><ul><li>Shear modulus </li></ul><ul><li>Reinforcement </li></ul>
    71. 71. Condition Assessment <ul><li>Visual examination </li></ul><ul><ul><li>measure dimensions </li></ul></ul><ul><ul><li>identify construction type </li></ul></ul><ul><ul><li>identify materials </li></ul></ul><ul><ul><li>identify connection types </li></ul></ul><ul><li>Knowledge factor </li></ul><ul><ul><li> = 0.75 when visual exam is done </li></ul></ul>
    72. 72. Condition Assessment <ul><li>Nondestructive tests </li></ul><ul><ul><li>ultrasonic </li></ul></ul><ul><ul><li>mechanical pulse velocity </li></ul></ul><ul><ul><li>impact echo or radiography </li></ul></ul><ul><li>Knowledge factor </li></ul><ul><ul><li> = 1.00 with comprehensive knowledge level </li></ul></ul>
    73. 73. Movements
    74. 74. Differential Movements <ul><li>One common cause of cracking is differential movement between wythes. </li></ul>Ref: BIA Tech. Note 18 Movement - Volume Changes and Effect of Movement, Part I <ul><li>Clay masonry expands </li></ul><ul><li>Consider differential movements relative to steel or concrete frames </li></ul><ul><li>Different materials expand or contract different amounts due to: </li></ul><ul><ul><li>temperature </li></ul></ul><ul><ul><li>humidity </li></ul></ul><ul><ul><li>freezing </li></ul></ul><ul><ul><li>elastic strain </li></ul></ul><ul><li>Cementitious materials shrink and creep </li></ul>shrink expand
    75. 75. Coefficients of Thermal Expansion Thermal coefficients for other structural materials can be found in BIA Technical Note 18. Concrete Masonry dense aggregate 5.2 0.62 Stone granite 4.7 0.56 fire clay brick or tile 2.5 0.30 clay or shale tile 3.3 0.40 cinder aggregate 3.1 0.37 expanded shale aggregate 4.3 0.52 expanded slag aggregate 4.6 0.55 pumice or cinder aggregate 4.1 0.49 limestone 4.4 0.53 marble 7.3 0.88 Clay Masonry clay or shale brick 3.6 0.43 Material Ave. Coefficient of Linear Thermal Expansion (x 10 -6 strain/ o F) Thermal Expansion (inches per 100’ for 100 o F temperature increase)
    76. 76. Moisture Movements <ul><li>Many masonry materials expand when their moisture content is increased, and then shrink when drying. </li></ul>Moisture Expansion of Clay Masonry = 0.020% Freezing Expansion of Clay Masonry = 0.015% <ul><li>Moisture movement is almost always fully reversible, but in some cases, a permanent volume change may result. </li></ul>
    77. 77. Moisture Movements in Concrete Masonry <ul><li>Because concrete masonry units are susceptible to shrinkage, ASTM limits the moisture content of concrete masonry depending on the unit’s linear shrinkage potential and the annual average relative humidity. For Type I units the following table is given. </li></ul>Moisture Content, % of Total Absorption (average of three units) Linear Shrinkage, % Humidity Conditions at Job Site humid intermediate arid 0.03 or less 45 40 35 0.03 to 0.045 40 35 30 0.045 to 0.065 35 30 25
    78. 78. Control Joints in Concrete Masonry <ul><li>Control joints designed to control shrinkage cracking in masonry. </li></ul>Spacing recommendations per ACI for Type I moisture controlled units. Cut spacing in half for Type II and reduce by one-third for solidly grouted walls. Vertical S pacing of Joint Reinforcement Recommended control joint spacing None 24” 16” 8” Ratio of panel length to height, L/h 2 2.5 3 4 Panel length in feet (not to exceed L regardless of H) 40 45 50 60
    79. 79. Control Joints in Concrete Masonry <ul><li>Control joints should be placed at: </li></ul><ul><ul><li>all abrupt changes in wall height </li></ul></ul><ul><ul><li>all changes in wall thickness </li></ul></ul><ul><ul><li>coincidentally with movement joints in floors, roofs and foundations </li></ul></ul><ul><ul><li>at one or both sides of all window and door openings </li></ul></ul>
    80. 80. Control Joint Details for Concrete Masonry Ref. NCMA TEK 10-2A Control Joints in Concrete Masonry Walls control joint unit grout fill paper raked head joint and caulk
    81. 81. Expansion Joints in Clay Masonry Pressure-relieving or expansion joints accommodate expansion of clay masonry. Ref: Masonry Design and Detailing , Christine Beall, McGraw-Hill BIA Tech. Note 18A Movement - Design and Detailing of Movement Joints, Part II expansion joint
    82. 82. Spacing of Expansion Joints For brick masonry: where W = total wall expansion in inches 0.0002 = coefficient of moisture expansion 0.0000043 = coefficient of thermal expansion L = length of wall in inches T max = maximum mean wall temperature, °F T min = minimum mean wall temperature, °F L )] T T ( 0000045 . 0 0002 . 0 [ W min max    min max T T ) p ( 000 , 24 S   S = maximum spacing of joints in inches p = ratio of opaque wall area to gross wall area
    83. 83. Expansion Joint Details for Brick Veneer Walls 20 oz. copper silicone or butyl sealant neoprene extruded plastic
    84. 84. Vertical Expansion of Veneer rc beam concrete block joint reinforcement or wire tie clay-brick veneer compressible filler flashing with weep holes steel shelf angle 1/4” to 3/8” min. clearance
    85. 85. Expansion Problems In cavity walls, cracks can form at an external corner because the outside wythe experiences a larger temperature expansion than the inside wythe. sun
    86. 86. Expansion Problems <ul><li>Diagonal cracks often occur between window and door openings if differential movement is not accommodated. </li></ul>
    87. 87. Expansion Problems <ul><li>Clay-unit masonry walls or veneers can slip beyond the edge of a concrete foundation wall because the concrete shrinks while the clay masonry expands. As a result, cracks often form in the masonry at the corner of a building. </li></ul>Concrete Foundation Brick Veneer Concrete Foundation Brick Veneer
    88. 88. Expansion Problems <ul><li>Brick parapets are sensitive to temperature movements since they are exposed to changing temperatures on both sides. </li></ul>parapet roof sun Elongation will be longer than for wall below.
    89. 89. End of Lessons 2 and 3

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